A Review of the Geological Characteristics of 'Gold-Only' Deposits in the Superior Province of the Canadian Shield

Of the 135 current or past-producing 'gold-only' mines in the Superior Province of the Canadian Shield which have produced more than 100,000 tons of ore, the 33 mines which have produced one million ounces or more of gold have accounted for over 84o/o of the total production of 137 million ounces. The published literature on these 33 deposits was reviewed in order to determine the geological setting of the mineralization on a regional (mining camp) and local (mine) scale. The dominant rock types underlying the mining camps are mafic, variolitic, tholeiitic volcanic rocks with a significant ultramafic (komatiitic) component, and clastic and/ or exhalative sedimentary rocks. Felsic volcanic rocks are generally subordinate. Most mining camps are located at or near the top of the mafic-ultramafic sequence, and generally there is a majorsedimentary-volcanic contact present which may be 1) a stratigraphic superposition of volcanic and sedimentary units, 2) a rapid, along-strike gradation from dominantly volcanic to dominantly sedimentary units due to facies change, or to the formation of structurally controlled sedimentary basins during volcanism, or 3) frequently (at 40o/o of the camps) a juxtaposition of sedimentary and volcanic sequences across a major fault zone or 'break', which in many instances may represent a reactivated, syn-volcanic basin-margin fault.In contrast to the regional setting, on a local or mine scale over 90o/o of the 33 mines contain felsic intrusions and/ or extrusions within mine workings. The felsic rocks may be quartzbearing (commonly quartz-feldspar porphyries) or dominantly quartz-free (commonly feldspar porphyry syenites or monzonites), and appear to have been emplaced in two different depth-zone environments: an epizonal intrusive environment, and a volcanic vent environment. Although the distinction between epizonal intrusive and volcanic intrusive-extrusive rocks is uncertain in many deposits, the two are tentatively separated on the basis of the grain size of the rock matrix (medium to coarse grained vs aphanitic to fine grained), homogeneity (multi-phased and/ or compositionally zoned vs compositionally homogeneous), and the shape and relationship to stratigraphy of the igneous body (circular or oval in cross section, and cutting the stratigraphy at a low angle vs lenticular and either stratiform or cutting the stratigraphy at a high angle). In addition, felsic intrusions of the volcanic environment commonly grade into tuffs or breccias of extrusive origin, whereas epizonal intrusions do not. Stratiform ore zones of possible exhalative sedimentary origin appear to be confined to deposits in which volcanic felsic rocks are present, and are absent from deposits in which only epizonal felsic intrusions are present. Pervasive carbonate- rich alteration, commonly in roughly stratabound zones of regional extent, and carbonate-rich chemical sedimentary rocks are present in over three-quarters of the deposits containing quartz-bearing felsic volcanic rocks, but are much less common in deposits with quartz-free felsic volcanic rocks. The Gold Deposits host sequences of epizonal felsic intrusions which are quartzfree are more commonly sedimentary than those of quartzbearing epizonal felsic intrusions. Quartz, carbonate minerals, arsenopyrite, scheelite, tourmalineand Cr-muscovite ('juchsite') are the most common mineralogical associates of gold. Arsenopyrite is essentially restricted to the volcanic environment, occurring in about twothirds of the deposits with quartz-bearing felsic volcanic rocks and less than half of the deposits with quartz-free volcanic rocks. Tourmaline, on the other hand, is almost ubiquitous in deposits associated with epizonal intrusions and also occurs in about two-thirds of the deposits associated with quartz-bearing felsic volcanic rocks, but in only one of the eight deposits associated with quartz-free felsic volcanic rocks. Scheelite is essentially restricted to ores of quartz-rich felsic association. Exploration for new gold mining camps should be concentrated in the upper parts of mafic-ultramafic volcanic sequences, and especially at the contact zones of these sequences with clastic and/ or exhalative sedimentary rock sequences. In this general environment, the presence of interfingering or juxtaposed volcanic and sedimentary rock units, large zones of carbonate alteration of the volcanic rocks and/ or carbonateor sulphide-rich chemical sedimentary rocks, and small felsic intrusive or extrusive bodies, are favourable indicators for the occurrence of deposits with stratiform, possibly chemical sedimentary gold ore zones. Epizonal intrusives of stock to small batholith size and their contact zones are favourable for deposits containing only epigenetic vein and replacement-type ore zones. Arsenopyrite, scheelite, Cr-muscovite ('juchsite') and tourmaline are favourable indicator minerals for gold mineralization in all environments.

Fluid inclusion studies from the Cinola deposit indicate low salinities and low C01 contents of the ore fluid. This supports a suggestion that the mineralizing fluids originated from pore water in the fluviatile host rock (mid-Miocene Skonun Formation). Bimodal distribution of filling temperatures suggests the existence of at least two temperature regimes centred on 160°C and 270°C during mineral deposition. Independent age and stratigraphic evidence indicates that depth of mineralization is...

In the Timmins area, a close spatial and chronological association exists between gold deposits and two major stratabound carbonate-rich members and related quartz-feldspar porphyries. Synvolcanic and metamorphogenic are the two main types of mineralization recognized. Synvolcanic ores include the stratiform quartz-ankerite "veins", pyritic carbonates and chert-carbonate-tuff sedimentary rocks and epigenetic ventrelated breccias and stringer zones. Metamorphogenic ores consist of quartz-carbo...

Preliminary investigations indicate that organic lake sediments offer some potential for gold exploration within the Canadian Shield of northwestern Saskatchewan. It is also apparent that certain precautions must be taken. Gold is primarily related to the organic fraction of the lake sediments, which, although giving consistant Au contents to those sediments, may restrict the dispersion of Au within the lake itself. It may be necessary to carry out selective extractions on the lake sediments...

Publication:

Special Volume

Author(s):

WILLIAM B. COKER Geological Survey of Canada, J.S. FOX Saskatchewan Mining Development Corp., and VLADIMIR J. SOPUCK Saskatchewan Research Council

The major Archean gold deposits in the Red Lake greenstone belt, which have produced over 374 million grams of gold since 1930, occur near the top of the lower komatiitic to tholeiitic mafic to ultramafic metavolcanic sequence. The upper calalkalic to felsic rocks form three discrete and separate ediftces overlymg this lower sequence. The gold deposits are classified according to their stratigraphic or lithologic associations into:1) mafic-volcanic-hosted deposits;2) felsic-intrusive-hosted...

In February 1980, Dome Mines Limited announced a $50 million expansion program which would result in a 50% increase in mill capacity from the present 1,815 tonnes per day to an eventual production rate of 2, 720 tonnes per day in the year 1984. As an integral and necessary part of this planned expansion, a new vertical production shaft, No. 8 Shaft, would be sunk from surface to a depth of 1,645 metres. Throughout the seventy-year history of mining at the Dome, gold has been found in a number...

Although C02 content indicates the quantity of carbonate in altered basaltic rocks, it does not measure the intensity of carbonate alteration. CO/CaO molar ratios, which correlate with the relative proportions of individual carbonate species, measure the intensity of carbonatization. The Timmins gold area is characterized by pervasive carbonatization, with large parts of the area having C02/Ca0 ratios greater than 1, representing C02 supersaturation relative to CaO. The mean CO/CaO in the...

All gold deposits within the Tisdale Group are spatially associated with carbonate alteration zones; however, not all carbonate alteration zones are host to gold mineralization. Within the komatiitic and magnesium tholeiitic volcanic rocks at the base of the Tisdale Group, discordant and stratabound carbonate alteration zones occur throughout. The alteration zones consist of a ferroan dolomite - quartz inner assemblage which is enveloped by calcite-quartz and an outer chlorite-rich subzone....

The Upper Beaver Mine, Kirkland Lake, Ontario, is a copper-gold deposit in mafic flows and sedimentary rocks. The deposit consists of a number of orebodies of two types: copper- and gold-bearing chalcopyrite-pyrite-magnetite ore; and gold-bearing quartz veins. Chalcopyrite-pyrite-magnetite ore occurs in two structural forms: as cherty interjlow material in coarse clastic roks underlying flows; and as veins. Both sedimentary and vein ore occur in each orebody. The goldbearing quartz veins...

The Doyon Mine gold deposits in Bousquet township occur in a felsic pyroclastic horizon of the Archean Blake River Group. Initial work outlined zone number I, within a lapilli tuff, and zone number 2, mainly within the underlying blocky tuff Zone number 2 has been mined by open pit since February 1980. The lapilli tuff around number I is intensely altered to sericite and carries abundant pyrite; gold is fine grained in the silicate minerals in close association with pyrite. In zone number 2,...

Between 1934 and 1956, nearly 31 million grams of gold were produced in the Matachewan area from deposits on properties belonging to Young-Davidson Mines Limited and Matachewan Consolidated Mines Limited. In 1979, production from these properties was renewed by Pamour Porcupine Mines Limited. Most of the gold produced has come from relatively lowgrade deposits (3.4 gl t or less) that occur in an east-trending belt of dykes and irregular bodies of trachytic syenite. Although small by compariso...

The Bousquet deposit consists of a number of stratiform lenses of pyrite with gold as native metal and as telluride minerals in volcanic rocks of the Archean Abitibi Greenstone Belt, 6.5 km north of Cadillac, Quebec. The Number 3 lens, which went into production in 1979, contains 1 million tonnes grading 7.5 grams of gold per tonne. It is 500 m long, 6 m thick and consists of recrystallized quartz with 2-mm-thick anastomosing layers of graphite and muscovite averaging 8 per cent subhedral...

The Bousquet deposit consists of a number of stratiform lenses of pyrite with gold as native metal and as telluride minerals in volcanic rocks of the Archean Abitibi Greenstone Belt, 6.5 km north of Cadillac, Quebec. The Number 3 lens, which went into production in 1979, contains 1 million tonnes grading 7.5 grams of gold per tonne. It is 500 m long, 6 m thick and consists of recrystallized quartz with 2-mm-thick anastomosing layers of graphite and muscovite averaging 8 per cent subhedral...

The gold ore zones of the Campbell and Dickenson mines occur within a km-wide, 2 km-long zone of highly altered and anomalously fissile and deformed volcanic and subvolcanic intrusive rocks, cut by a series of mainly post-deformation mafic and quartz-feldspar porphyry felsic dykes. Three main periods of gold ore-forming hydrothermal activity are recognized. In the first, the mine rocks were extensively altered and gold and arsenic enriched; syn-volcanic auriferous veinlet and low-grade...

Archean lode gold deposits of both vein and chemical sedimentary types typically have major enrichments of certain rare elements, including Au, Ag, As, Sb, B, W, Se, Te and Bi, coupled with low or negative enrichments of the more abundant and mobile base metals, Cu, Pb and Zn. On the other hand, in massive base metal sulphide deposits Au, Ag, Cu, Zn and in some instances Pb are all enriched by a factor of 200 to 2000 compared to background and there is no large separationof gold relative to...

Publication:

Special Volume

Author(s):

R. KERRICH and R.W. HODDER Department of Geology, University of Western OntarioLondon, Ontario

The Chadbourne mine is within the town of Noranda, Rouyn Township, Quebec. After attempts in 1923, 1932, 1951 and 1969, production began in January 1978, with reserves of 1.1 million tonnes of 4.52 g Au/ tonne plus trace amounts of silver, copper and zinc. This deposit is in the northern twothirds of a breccia which cuts felsic and mafic metavolcanic rocks of the Blake River Group, within the Archean Abitibi Greenstone Belt. The breccia is elliptical at surface, 300 m from north to south and...

In a continuing program of mapping glacial dispersal trains, near-surface till samples were collected down-ice from a copper-silver-gold prospect at Onaman River, Ontario, and down-ice from the past-producing gold district at Oldham, Nova Scotia. The program is designed to aid exploration by illustrating glacial dispersal from various types of known occurrences and by identifying postglacial processes that control drift composition at a detailed scale. Native gold was mined at Oldham from...

Gold has been reported from most geological environments in Nova Scotia; however, virtually all production (circa 2,000, 000 troy ounces; circa 60 tonnes) has come from that part of the province to the south of the Glooscap Fault which is underlain by Lower Paleozoic rocks of the Meguma Group. Over fifty concordant sets of quartz-carbonate-arsenopyrite veins haveseen production. The host rocks are greenschist-grade equivalents of Cambro-Ordovician flyschoid quartz wackes and shales folded...

The Bousquet region now contains three producing gold mines and has the potential of becoming one of the major gold producing regions of the Abitibi greenstone belt. Gold occurs in three distinct geological settings. Firstly, auriferous, stratiform and stratified quartz-muscovite-pyrite bodies or massive pyritic lenses such as at Dumagami, Bousquet and Silvers tack are situated along the north limb of the Cadillac syncline at the stratigraphic top of the Blake Riv_er Group, a predominantly...

Publication:

Special Volume

Author(s):

R.I. VALLIANT and R.W. HUTCHINSON, Department of Geology, University of Western Ontario, London, Ontario